Tweening-based codec for scaleable encoders and decoders with varying motion computation capability

ABSTRACT

A scaleable video encoder has one or more encoding modes in which at least some, and possibly all, of the motion information used during motion-based predictive encoding of a video stream is excluded from the resulting encoded video bitstream, where a corresponding video decoder is capable of performing its own motion computation to generate its own version of the motion information used to perform motion-based predictive decoding in order to decode the bitstream to generate a decoded video stream. All motion computation, whether at the encoder or the decoder, is preferably performed on decoded data. For example, frames may be encoded as either H, L, or B frames, where H frames are intra-coded at full resolution and L frames are intra-coded at low resolution. The motion information is generated by applying motion computation to decoded L and H frames and used to generate synthesized L frames. L-frame residual errors are generated by performing inter-frame differencing between the synthesized and original L frames and are encoded into the bitstream. In addition, synthesized B frames are generated by tweening between the decoded H and L frames and B-frame residual errors are generated by performing inter-frame differencing between the synthesized B frames and, depending on the implementation, either the original B frames or sub-sampled B frames. These B-frame residual errors are also encoded into the bitstream. The ability of the decoder to perform motion computation enables motion-based predictive encoding to be used to generate an encoded bitstream without having to expend bits for explicitly encoding any motion information.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of the filing date of U.S.provisional application No. 60/172,841, filed on Dec. 20, 1999.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to video compression/decompression (codec)processing.

2. Description of the Related Art

Traditional video compression/decompression processing relies onasymmetric computation between the encoder and decoder. The encoder isused to do all the analysis of the video stream in terms of inter- andintra-frame components, including block-based motion computation, andalso in terms of object-based components. The analysis is used tocompress static and dynamic information in the video stream. The decodersimply decodes the encoded video bitstream by decompressing the intra-and block-based inter-frame information. No significant analysis isperformed at the decoder end. Examples of such codecs include MPEG1,MPEG2, MPEG4, H.263, and related standards. The quality of “codeced”video using the traditional asymmetric approach is reasonably good fordata rates above about 1.2 megabits/second (Mbps). However, the typicalquality of output video is significantly degraded at modem speeds of 56kilobits/second (Kbps) and even at speeds as high as a few 100 Kbps.

SUMMARY OF THE INVENTION

The present invention is related to video compression/decompressionprocessing that involves analysis of the video stream (e.g., motioncomputation) at both the encoder end and the decoder end. With the rapidincrease in processing power of commonly available platforms, and withthe potential for dedicated video processing sub-systems becomingviable, the techniques of the present invention may significantlyinfluence video delivery on the Internet and other media at low andmedium bit-rate channels.

In traditional video compression, any and all motion computation isperformed by the encoder, and none by the decoder. For example, in aconventional MPEG-type video compression algorithm, for predictiveframes, the encoder performs block-based motion estimation to identifymotion vectors that relate blocks of data in a current frame to closelymatching blocks of reference data for use in generatingmotion-compensated inter-frame differences. These inter-framedifferences (also referred to as residual errors) along with the motionvectors themselves are explicitly encoded into the resulting encodedvideo bitstream. Under this codec paradigm, without having to performany motion computation itself, a decoder recovers the motion vectors andinter-frame differences from the bitstream and uses them to generate thecorresponding frames of a decoded video stream. As used in thisspecification, the term “motion computation” refers to motion estimationand other types of analysis in which motion information for videostreams is generated, as opposed to motion compensation, where alreadyexisting motion information is merely applied to video data.

According to certain embodiments of the present invention, a videodecoder is capable of performing at least some motion computation. Assuch, the video encoder can omit some or all of the motion information(e.g., motion vectors) from the encoded video bitstream, relying on thedecoder to perform its own motion computation analysis to generate theequivalent motion information required to generate the decoded videostream. In this way, more of the available transmission and/or storagecapacity (i.e., bit rate) can be allocated for encoding the residualerrors (e.g., inter-frame differences) rather than having to expend bitsto encode motion information.

According to one embodiment, the present invention is a method forencoding a video stream to generate an encoded video bitstream,comprising the steps of (a) encoding, into the encoded video bitstream,a first original frame/region in the video stream using intra-framecoding to generate an encoded first frame/region; and (b) encoding, intothe encoded video bitstream, a second original frame/region in the videostream using motion-based predictive coding, wherein at least somemotion information used during the motion-based predictive coding isexcluded from the encoded video bitstream.

According to another embodiment, the present invention is a videoencoder for encoding a video stream to generate an encoded videobitstream, comprising (a) a frame/region type selector configured forselecting different processing paths for encoding differentframes/regions into the encoded video bitstream; (b) a first processingpath configured for encoding, into the encoded video bitstream, a firstoriginal frame/region in the video stream using intra-frame coding togenerate an encoded first frame/region; and (c) a second processing pathconfigured for encoding, into the encoded video bitstream, a secondoriginal frame/region in the video stream using motion-based predictivecoding, wherein the video encoder has an encoding mode in which at leastsome motion information used during the motion-based predictive codingis excluded from the encoded video bitstream.

According to yet another embodiment, the present invention is a methodfor decoding an encoded video bitstream to generate a decoded videostream, comprising the steps of (a) decoding, from the encoded videobitstream, an encoded first frame/region using intra-frame decoding togenerate a decoded first frame/region; and (b) decoding, from theencoded video bitstream, an encoded second frame/region usingmotion-based predictive decoding, wherein at least some motioninformation used during the motion-based predictive decoding isgenerated by performing motion computation as part of the decodingmethod.

According to yet another embodiment, the present invention is a videodecoder for decoding an encoded video bitstream to generate a decodedvideo stream, comprising (a) a frame/region type selector configured forselecting different processing paths for decoding different encodedframes/regions from the encoded video bitstream; (b) a first processingpath configured for decoding, from the encoded video bitstream, anencoded first frame/region in the video stream using intra-framedecoding to generate a decoded first frame/region; and (c) a secondprocessing path configured for decoding, from the encoded videobitstream, an encoded second frame/region in the video stream usingmotion-based predictive decoding, wherein the video decoder has adecoding mode in which at least some motion information used during themotion-based predictive decoding is generated by the video decoderperforming motion computation.

According to yet another embodiment, the present invention is a methodfor decoding an encoded video bitstream to generate a decoded videostream, comprising the steps of (a) decoding, from the encoded videobitstream, a plurality of encoded frames/regions to generate a pluralityof decoded frames/regions using motion information; and (b) performingtweening based on the motion information to insert one or moreadditional frames/regions into the decoded video stream.

According to yet another embodiment, the present invention is a decoderfor decoding an encoded video bitstream to generate a decoded videostream, comprising (a) one or more processing paths configured fordecoding, from the encoded video bitstream, a plurality of encodedframes/regions to generate a plurality of decoded frames/regions usingmotion information; and (b) an additional processing path configured forperforming tweening based on the motion information to insert one ormore additional frames/regions into the decoded video stream.

BRIEF DESCRIPTION OF THE DRAWINGS

Other aspects, features, and advantages of the present invention willbecome more fully apparent from the following detailed description, theappended claims, and the accompanying drawings in which:

FIG. 1 shows a block diagram of a scaleable video encoder, according toone embodiment of the present invention;

FIG. 2 shows a representation of the encoding of an input video streamby the video encoder of FIG. 1;

FIG. 3 shows a flow diagram of the processing of each H frame by thevideo encoder of FIG. 1;

FIG. 4 shows a flow diagram of the processing of each L frame by thevideo encoder of FIG. 1;

FIG. 5 shows a flow diagram of the processing of each B frame by thevideo encoder of FIG. 1;

FIG. 6 shows a block diagram of a video decoder, according to oneembodiment of the present invention;

FIG. 7 shows a flow diagram of the processing of each L frame by thevideo decoder of FIG. 6;

FIG. 8 shows a flow diagram of the processing of each B frame by thevideo decoder of FIG. 6;

FIG. 9 represents a basketball event being covered by a ring of cameras;and

FIG. 10 represents a space-time continuum of views along the ring ofcameras of FIG. 9.

DETAILED DESCRIPTION

In current state-of-the-art motion video encoding algorithms, like thoseof the MPEGx family, a large part of the bit budget and hence thebandwidth is consumed by the encoding of motion vectors and error imagesfor the non-intra-coded frames. In a typical MPEG2 coded stream,approximately 5% of the bit budget is used for overhead, 10-15% is forintra-coded frames (i.e., frames that are coded as stills), 20-30% isfor motion vectors, and 50-65% of the budget is for error encoding. Therelatively large budget for error encoding can be attributed to two mainreasons. First, motion vectors are computed only as a translation vectorfor (8×8) blocks or (16×16) macroblocks, and, second, the resultingerrors tend to be highly uncorrelated and non-smooth.

According to certain embodiments of the present invention, motioncomputation is performed at both the encoder end and the decoder end. Assuch, motion information (e.g., motion vectors) need not be transmitted.Since motion computation is performed at the decoder end, instead oflimiting the representation of motion to block-based translations,motion fields can be computed with greater accuracy using a combinationof parametric and non-parametric representations.

Embodiments of the present invention enable the video stream to besub-sampled both temporally and spatially at the encoder. The videostream can be sub-sampled in time so that not all of the frames aretransmitted. In addition, some of the frames that are transmitted may becoded at a lower spatial resolution. Using dense and accurate motioncomputation at the decoder end, the decoded full-resolution andlow-resolution frames are used to recreate a full-resolution decodedvideo stream with missing frames filled in using motion-compensatedspatio-temporal interpolation (also referred to as “tweening”). Thiscould result in large savings in compression while maintaining qualityof service for a range of different bandwidth pipes.

In one embodiment of the present invention, a scaleable encoder iscapable of encoding input video streams at a number of differentencoding modes corresponding to different types of decoders, e.g.,having different levels of processing capacity.

At one extreme class of encoding modes, the encoder generates an encodedvideo bitstream for a decoder that is capable of performing all of themotion computation performed by the encoder. In that case, the encoderencodes the video stream using an encoding mode in which motion-basedpredictive encoding is used to encode at least some of the frames in thevideo stream, but none of the motion information used during the videocompression processing is explicitly included in the resulting encodedvideo bitstream. The corresponding decoder performs its own motioncomputation during video decompression processing to generate its ownversion of the motion information for use in generating a decoded videostream from the encoded video bitstream, without having to rely on thebitstream explicitly carrying any motion information.

At the other extreme class of encoding modes, the encoder encodes thevideo stream for a decoder that is incapable of performing any motioncomputation (as in conventional video codecs). In that case, if theencoder uses any motion information during encoding (e.g., formotion-compensated inter-frame differencing), then all of that motioninformation is explicitly encoded into the encoded video bitstream. Thecorresponding decoder recovers the encoded motion information from theencoded video bitstream to generate a decoded video stream withouthaving to perform any motion computation on its own.

In between these two extremes are a number of different encoding modesthat are geared towards decoders that perform some, but not all of themotion computation performed by the encoder. In these situations, theencoder explicitly encodes some, but not all of the motion informationused during its motion-based predictive encoding, into the resultingvideo bitstream. The corresponding decoder recovers the encoded motioninformation from the bitstream and performs its own version of motioncomputation to generate the rest of the motion information used togenerate a decoded video stream.

Independent of how much motion information is to be encoded into thebitstream, a scaleable encoder of the present invention is also capableof skipping frames with the expectation that the decoder will be able toinsert frames into the decoded video stream during playback. Dependingon the implementation, frame skipping may involve providing at leastsome header information for skipped frames in the encoded videobitstream or even no explicit information at all.

Encoding

FIG. 1 shows a block diagram of a scaleable video encoder 100, accordingto one embodiment of the present invention. Scaleable video encoder 100will first be described in the context of an extreme encoding mode inwhich none of the motion information used during motion-based predictiveencoding is explicitly encoded into the resulting encoded videobitstream. Other encoding modes will then be described.

According to this extreme encoding mode, each frame in an input videostream is encoded as either an H frame, an L frame, or a B frame. Each Hframe is intra-encoded as a high spatial resolution (e.g.,full-resolution) key frame, each L frame is intra-encoded as a lowspatial resolution (e.g., ¼×¼ resolution) key frame augmented byresidual error encoding, and each B frame is inter-encoded as a lowspatial resolution frame based on motion estimates between sets of Hand/or L frames. Video encoder 100 encodes an input video stream as asequence of H, L, and B frames to form a corresponding output encodedvideo bitstream.

FIG. 2 shows a representation of a particular example of the encoding ofan input video stream by video encoder 100 of FIG. 1. In the example ofFIG. 2, the input video stream is encoded using a repeating 10-framesequence of (HBLBLBLBLB). In general, however, other fixed or evenadaptive frame sequences are possible. For example, in one preferredfixed frame sequence, a 30 frame/second (fps) video stream is encodedusing the fixed 30-frame sequence of:

 (HBBBBBLBBBBBLBBBBBLBBBBBLBBBBB).

The generation of the frame-type sequence may also be performedadaptively, e.g., based on the amount of motion present across frame,with fewer B frames between consecutive H/L key frames and/or fewer Lframes between consecutive H frames when motion is greater and/or lessuniform, and vice versa.

Referring again to FIG. 1, type selection 102 is applied to the inputvideo stream to determine which frames in the video stream are to beencoded as H, L, and B frames. (Although this type selection 102 will bedescribed in the context of entire frames, this process may also beimplemented based on regions within a frame, such as square blocks,rectangular regions, or even arbitrary shaped regions, with thecorresponding estimation and encoding applied to each.) As mentionedabove, depending on the particular implementation, the frame-typeselection may be based on a fixed frame sequence or an appropriateadaptive selection algorithm, e.g., based on motion magnitude, specialeffects, scene cuts, and the like. Each of the different types of framesis then processed along a corresponding processing path represented inFIG. 1. As shown in FIG. 1, an option exists to drop one or more framesfrom the input video stream. This optional frame dropping may beincorporated into a fixed frame sequence or adaptively selected, e.g.,based on the amount of motion present or bit-rate considerations.

FIG. 3 shows a flow diagram of the processing of each H frame by videoencoder 100 of FIG. 1. Referring to the blocks in FIG. 1 and the stepsin FIG. 3, the current H frame is intra-encoded at full resolution,e.g., using wavelet encoding (block 104 of FIG. 1 and step 302 of FIG.3). As is known in the art, wavelet encoding typically involves theapplication of wavelet transforms to different sets of pixel datacorresponding to regions within a current frame, followed byquantization, run-length encoding, and variable-length (Huffman-type)encoding to generate the current frame's contribution to the encodedvideo bitstream. Typically, the sizes of the regions of pixel data (andtherefore the sizes of the wavelet transforms) vary according to thepixel data itself. In general, the more uniform the pixel data, thelarger the size of a region that is encoded with a single wavelettransform. Note that even though this encoding is referred to as “fullresolution,” it may still involve sub-sampling of the color components(e.g., 4:1:1 YUV sub-sampling).

The resulting intra-encoded full-resolution H-frame data is incorporatedinto the encoded video bitstream (step 304). The same intra-encodedH-frame data is also decoded (block 106 and step 306), e.g., usingwavelet decoding, to generate a full-resolution decoded H frame for useas reference data for encoding L and B frames.

FIG. 4 shows a flow diagram of the processing of each L frame by videoencoder 100 of FIG. 1. Referring to the blocks in FIG. 1 and the stepsin FIG. 4, the current full-resolution L frame is spatially sub-sampled(e.g., by a factor of 4 in each direction) to generate a correspondinglow-resolution L frame (block 108 and step 402). Depending on theparticular implementation, this spatial sub-sampling may be based on anysuitable technique, such as simple decimation or more complicatedaveraging.

The low-resolution L frame is then intra-encoded (block 110 and step404), e.g., using wavelet encoding, and the resulting intra-encodedlow-resolution L-frame data is incorporated into the encoded videobitstream (step 406). The same intra-encoded L-frame data is alsodecoded to generate a decoded low-resolution L frame (block 112 and step408).

Motion computation analysis is then performed comparing the decodedlow-resolution L-frame data to one or more other sets of decoded data(e.g., decoded full-resolution data corresponding to the previous and/orsubsequent H frames and/or decoded low-resolution data corresponding tothe previous and/or subsequent L frames) to generate motion informationfor the current L frame (block 114 and step 410). In this particular“extreme” encoding mode, none of this L-frame motion information isexplicitly encoded into the encoded video bitstream. In other encodingmodes (including the opposite “extreme” encoding mode), some or all ofthe motion information is encoded into the bitstream (step 412).

The exact type of motion computation analysis performed depends on theparticular implementation of video encoder 100. For example, motion maybe computed for each L frame based on either the previous H frame, theclosest H frame, or the previous key (H or L) frame. Moreover, thismotion computation may range from conventional MPEG-like block-based ormacroblock-based algorithms to any of a combination of optical flow,layered motion, and/or multi-frame parametric/non-parametric algorithms.

For example, in one implementation, video encoder 100 may performconventional forward, backward, and/or bi-directional block-based motionestimation in which a motion vector is generated for each (8×8) block or(16×16) macroblock of pixels in the current frame. In alternativeembodiments, other types of motion computation analysis may beperformed, including optical flow analysis in which a different motionvector is generated for each pixel in the current frame. (For thoseencoding modes in which some or all of the motion information is encodedinto the bitstream, the optical flow can be compactly represented usingeither wavelet encoding or region-based parametric plus residual flowencoding.) Still other implementations may rely on hierarchical orlayered motion analysis in which a number of different motion vectorsare generated at different resolutions, where finer motion information(e.g., corresponding to smaller sets of pixels) provide corrections tocoarser motion information (e.g., corresponding to larger sets ofpixels). In any case, the resulting motion information characterizes themotion between the current L frame and corresponding H/L frames.

No matter what type of analysis is performed, the motion informationgenerated during the motion computation is then used to synthesize afull-resolution L frame (block 116 and step 414). In particular, themotion information is used to warp (i.e., motion compensate) thecorresponding decoded full-resolution H frame to generate a synthesizedfull-resolution frame corresponding to the current L frame. Note thatthe synthesized full-resolution L frame may be generated using forward,backward, or even bi-directional warping based on more than one decodedfull-resolution H frame. This would require computation of motioninformation relative to two different decoded full-resolution H frames,but will typically reduce even further the corresponding residuals thatneed to be compressed.

In general, the synthesized full-resolution L frame may have artifactsdue to various errors in motion computation due to occlusions,mismatches, and the like. As such, a quality of alignment metric (e.g.,based on pixel-to-pixel absolute differences) is generated between thesynthesized full-resolution L frame and the original full-resolution Lframe (block 118 and step 416). The quality of alignment metrics form animage of residual errors that represent the quality of alignment at eachpixel.

The residual errors are then encoded for inclusion into the encodedvideo bitstream (block 120). In one implementation, the image ofresidual errors is thresholded at an appropriate level to form a binarymask (step 418) that identifies those regions of pixels for whom theresidual error should be encoded, e.g., using a wavelet transform, forinclusion into the encoded video bitstream (step 420). For typical videoprocessing, the residual errors for only about 10% of the pixels will beencoded into the bitstream.

FIG. 5 shows a flow diagram of the processing of each B frame by videoencoder 100 of FIG. 1. Referring to the blocks in FIG. 1 and the stepsin FIG. 5, the current full-resolution B frame is spatially sub-sampled(e.g., by a factor of 4 in each direction) to generate a correspondinglow-resolution B frame (block 122 and step 502). The low-resolutionmotion information generated based on the decoded H/L frame by block 114is used to perform interpolated motion compensation to synthesize alow-resolution frame for the current B frame (block 124 and step 504).In particular, the motion information generated by block 114 (i.e.,corresponding to the motion between the decoded H/L frame immediatelypreceding the current B frame and the decoded H/L frame immediatelyfollowing the current B frame) is temporally interpolated to generatemotion information for the current B frame. This temporally interpolatedmotion information is then used to perform forward, backward, orbi-directional motion compensation on those previous and subsequentdecoded H/L frames to generate the synthesized low-resolution B frame.This process of generating a synthesized B frame using temporallyinterpolated motion compensation is referred to as “tweening.”

Inter-frame differencing is then applied between the spatiallysub-sampled B frame and the low-resolution synthesized B frame togenerate low-resolution residual errors for the current B frame (block126 and step 506), which residual errors are then encoded, e.g., usingwavelet encoding, to generate encoded B-frame residual data forinclusion in the encoded video bitstream (block 128 and step 508).Depending on the particular implementation, the residual error encodingof block 128 may rely on a thresholding of B-frame inter-framedifferences to determine which residuals to encode, similar to thatdescribed previously with regard to block 120 for the L-frame residualerrors. Note that, since B frames are never used to generate referencedata for encoding other frames, video encoder 100 does not have todecode the encoded B-frame residual data.

In an alternative implementation of video encoder 100, instead ofsynthesizing low-resolution B frames, full-resolution B frames can besynthesized by tweening between pairs of decoded full-resolution Hframes generated by block 106 and synthesized full-resolution L framesgenerated by block 116. Inter-frame differencing can then be appliedbetween the original full-resolution B frames and the synthesizedfull-resolution B frames to generate residual errors that can beencoded, e.g., using wavelet encoding, into the encoded video bitstream.In that case, the spatial sub-sampling of block 122 can be omitted.

As mentioned earlier, the processing in FIGS. 3-5 correspond to theextreme encoding mode in which video encoder 100 performs motion-basedpredictive encoding, but none of the corresponding motion information isexplicitly encoded into the resulting encoded video bitstream, where thedecoder performs its own motion computation to generate its own versionof the motion information for use in generating the correspondingdecoded video stream. As mentioned earlier, video encoder 100 ispreferably a scaleable video encoder that can encode video streams at avariety of different encoding modes. Some of the encoding optionsavailable in video encoder 100 include:

-   -   Encoding frames as either H or L frames, without using any B        frames;    -   Dropping one or more B frames, while relying on the video        decoder to reconstruct dropped B frames by tweening between        appropriate encoded frames without relying on encoded residuals        for those B frames;    -   Encoding L frames using low-resolution intra-encoding without        explicitly encoding residual errors corresponding to errors in        synthesized L frames;    -   Encoding L frames using predictive encoding; and    -   Encoding some or even all of the motion information explicitly        into the encoded video bitstream.        Of course, if some or all of the motion information is to be        explicitly encoded into the bitstream, the video encoder will        need to be implemented with appropriate processing modules for        encoding that motion information into the encoded video        bitstream. In one possible encoding mode that generates        hierarchical or layered motion information, the encoder        explicitly includes only coarse motion information in the        encoded video bitstream. In that case, the decoder recovers the        coarse motion information and then performs its own motion        computation to generate the rest of the motion information        (e.g., fine or full-precision motion information). The exact        combination of encoding options to select for a particular input        video stream will depend on the computational power of the        decoder, the particular decompression algorithm implemented in        the decoder, the transmission and/or storage requirements (i.e.,        bit-rate requirements) for the encoded video bitstream, and/or        the required spatial and/or temporal quality of the decoded        video stream.        Variable Bit-Rate Adaptive Encoding

Scaleable video encoder 100 of FIG. 1 is highly amenable to adaptivevariable bit-rate encoding. The decision to increase or decrease thetemporal sampling rates of frames can be based on the magnitude ofmotion present between frames. Also, this decision can be based on thetype of motion between frames. For example, if within a clip the motioncan be captured quite adequately using global parametric transformations(e.g., camera pans), the sampling of frames may be coarser. If themotion is complex and of high magnitude, then sampling may need to befiner.

Furthermore, as mentioned previously, the nomenclature of H, L, and Bframes can be generalized so that it is applied at the level of regionswithin an image in addition to the frame level. This implies that framescan be divided into regions of varying motion magnitude, where regionsof large motion may be encoded more often than regions of smallermotion. This decision can be based both on the size of and magnitude ofmotion within a region. Therefore, typically a single frame may consistof regions encoded at the full resolution, regions encoded at lowerresolutions, and regions that are created by forward and backwardtweening of nearby frames.

Adaptive Encoding of Motion

Although motion encoding is avoided in some encoding modes, motion canbe selectively encoded to gain efficiency in the process. The decodermay be able to work at faster rates if motion estimates for seeding theprecise motion computation are available. Since the present invention isnot limited to block-based motion computation, the computation of themotion field between frames can be decomposed into multiple resolutions.At the coarsest level, there may be a global parametric fieldtransformation for the whole frame. At finer levels, the motion may beencoded either as a flow field or local parametric transformation at anappropriate resolution. The parametric transformation can be encodedalmost for free. The coarse motion fields may also be encoded usingwavelet encoding.

In general, motion encoding is an option for video encoder 100 and canbe used to enhance the time performance of the decoder. If some motionfields are provided to the decoder in the bitstream, then the decodercan refine the motion field further instead of starting from scratch.

Encoding the Interpolation Model for Tweening

Another piece of information that the encoder may compute is anappropriate model of tweening for the B frames. Since the decoder willuse nearby H and L frames to compute the B frames using tweening, theencoder can guide the decoder about the optimum model for interpolation.By computing models of motion change over a full frame/field, or withinadaptive windows, the encoder can direct the decoder to use variousinterpolation models suited for the data at hand, including linear,quadratic, cubic, and even higher-order interpolation models.

Decoding

As suggested earlier, the decoding algorithm for an encoded videobitstream generated using scaleable video encoder 100 of FIG. 1 dependson the particular encoding mode used to generate that encoded videobitstream. This section is directed primarily towards the decodingalgorithm corresponding to the “extreme” encoding mode represented inFIGS. 1 and 3-5, where no motion information is explicitly encoded intothe bitstream. Other decoding algorithms would be appropriately tailoredto the other encoding modes.

Referring again to FIG. 1, video encoder 100 performs motion computationonly on decoded data. In particular, the motion computation of block 114is applied to decoded full-resolution H frames and/or decodedlow-resolution L frames. Since the identical decoded data is generatedat the video decoder, the decoder is able to reconstruct the same motioninformation that was available at the encoder by performing its ownmotion computation analysis. This is not possible for prior artdecoders, since conventional lossy codec algorithms call for motioncomputation to be applied to the original input image data, which is notavailable at the decoder.

The video decoder almost exactly mirrors the analysis and synthesisperformed by the encoder. Instead of using the synthesizedfull-resolution frames only for encoding, the decoder creates thefull-resolution video stream. The encoding process dictates the decodingprocess. Motion is computed between the decoded low-resolution L framesand the closest decoded H frames. Full-resolution L frames aresynthesized by warping the relevant decoded H frame using the computedmotion information. In addition, areas of misalignment are detected asat the encoder, and these are filled in using the encodedfull-resolution L-frame residuals. This process generates a sequence ofdecoded H and L frames at full resolution. B frames are generated usingthe neighboring decoded H and L frames. If B-frame residuals areavailable from the bitstream, they are used to fill in the areas ofmisalignment in the B frames.

B frames are generated by tweening between appropriate decoded H andsynthesized L frames. There are a number of different models of flowinterpolation that tweening can employ. Constant velocity, constantacceleration, and adaptive models within given windows are just some ofthe choices that may be used. In addition, since the encoder can affordto compute motion information between every pair of frames, the encodedstream may be enhanced to contain information about the optimuminterpolation model for flow that the decoder should use. For example,if the motion is mostly a camera pan, then constant translation-basedinterpolation will suffice. Camera pan along with a significantly movingobject may require two different interpolation models within the sameframe. Such information can easily be encoded at the encoder end, sincedecisions about adaptive motion encoding need to be made anyway. Thedecoder will use the appropriate model for tweening.

It is assumed that the decoder and the encoder both have the capabilityto compute motion fields. This is not unreasonable at the decoder endgiven the rapidly increasing processing power of standard computingplatforms. Furthermore, this provides a unique opportunity to create acommodity-level video processor that may be included into everycomputing platform and set-top box.

Furthermore, the computed motion fields at the decoder end may be usedto interpolate new frames and create sequences with higher frame ratesand also to synthesize higher-resolution video frames.

If the encoded frames contain H, L, and B labels for regions within aframe in addition to the frames, then the decoder again mirrors theencoder's computation. It synthesizes a single frame by appropriatelychoosing high-resolution decoding for the H regions, motion-basedsynthesis of L regions, and tweening-based synthesis of B regions.

FIG. 6 shows a block diagram of a video decoder 600, according to oneembodiment of the present invention. Video decoder 600 decodes anencoded video bitstream generated by video encoder 100 of FIG. 1 togenerate a decoded video stream. As described earlier, the encoded videobitstream generated by video encoder 100 comprises encoded data for H,L, and B frames. Video decoder 600 performs frame/region type selection(block 602 in FIG. 6) (e.g., based on header information explicitlyencoded into the bitstream) to determine how to decode the various setsof encoded data. Although, as described previously, the encoder may makeH/L/B selections on the basis of regions within each frame, the presentdiscussion assumes that H/L/B selections were made by the encoder forentire frames.

For H frames, which the encoder has intra-encoded as full-resolutionframes, the corresponding encoded data are decoded (e.g., using waveletdecoding) to generate a corresponding decoded full-resolution H framefor the decoded video stream (block 604). This is identical to theanalogous processing performed by block 106 of video encoder 100.

FIG. 7 shows a flow diagram of the processing of each L frame by videodecoder 600 of FIG. 6. The encoded data corresponding to a current Lframe includes the intra-encoded low-resolution L frame data generatedat block 110 of FIG. 1 as well as the encoded L-frame residual datagenerated at block 120. Referring to the blocks in FIG. 6 and the stepsin FIG. 7, these encoded data are decoded to generate a decodedlow-resolution L frame and to recover the L-frame residual data (block606 of FIG. 6 and step 702 of FIG. 7). The generation of the decodedlow-resolution L frame is identical to the analogous processingperformed by block 112 of video encoder 100.

Video decoder 600 then performs motion computation for the currentlow-resolution L frame to generate motion information relative to one ormore decoded H/L frames (block 608 and step 704). This is identical tothe analogous processing performed by block 114 of video encoder 100.Since the data (e.g., the current low-resolution L frame as well asprevious and/or subsequent decoded full-resolution H frames) used by thedecoder to perform motion computation are identical to the data used bythe encoder to perform the analogous motion computation, the motioninformation generated by the decoder will be identical to the motioninformation generated by the encoder.

This motion information is then used to synthesize a full-resolution Lframe (block 610 and step 706). This is identical to the analogousprocessing performed by block 116 of video encoder 100. Inter-frameaddition is then performed to add the recovered L-frame residuals to thesynthesized full-resolution L frame to generate a decodedfull-resolution L frame for the decoded video stream (block 612 and step708).

FIG. 8 shows a flow diagram of the processing of each B frame by videodecoder 600 of FIG. 6. The encoded data corresponding to a current Bframe corresponds to the encoded B-frame residual data generated atblock 128 of FIG. 1. Referring to the blocks in FIG. 6 and the steps inFIG. 8, these encoded data are decoded to recover the B-frame residualdata (block 614 of FIG. 6 and step 802 of FIG. 8).

Video decoder 600 then performs tweening between decoded H and L framesto synthesize a low-resolution B frame (block 616 and step 804). This isidentical to the analogous processing performed by block 124 of videoencoder 100. Inter-frame addition is then performed to add the recoveredB-frame residuals to the synthesized low-resolution B frame to generatea decoded low-resolution B frame (block 618 and step 806).

Spatial up-sampling is then performed on the low-resolution decoded Bframe to generate a decoded full-resolution B frame for the decodedvideo stream (block 620 and step 808). The spatial up-sampling may relyon any suitable technique for generating a full-resolution image fromlow-resolution pixel data, including replication followed by spatialfiltering and other suitable one- or two-dimensional linear orhigher-order interpolation schemes.

Depending on the particular decoding mode, video decoder 600 cansynthesize additional frames into the decoded video stream, althoughthere will be no residual data to correct those synthesized frames, asindicated in FIG. 6 by the broken arrow from block 616 to block 620.

Since video encoder 100 is capable of encoding frames using backward andbi-directional prediction, the sequence of frames in the encoded videobitstream may differ from the sequence of frames in the input videostream. As such, video decoder 600 assembles the various decoded framesin their proper temporal order for presentation as the decoded videostream.

If, in an alternative codec algorithm, the B-frame residuals correspondto full-resolution errors rather than to low-resolution errors, then theB-frame synthesis of block 616 and step 804 would synthesizefull-resolution B frames and the inter-frame addition of block 618 andstep 806 would apply the full-resolution residuals to synthesizedfull-resolution B frames to generate decoded full-resolution B frames.In that case, the spatial up-sampling of block 620 and step 808 wouldnot be needed.

Independent of how much motion information, if any, is encoded into thebitstream, independent of the motion computation capabilities of thedecoder, independent of whether corresponding header information existsin the bitstream, and independent of whether the encoder even skippedcorresponding frames when generating the bitstream, a decoder accordingto certain embodiments of the present invention is capable of insertingframes into the decoded video stream during playback by performingtweening between decoded frames that are explicitly decoded from thebitstream, similar to the tweening described earlier for B frames.Unlike B frames, however, in the case of inserted frames, the bitstreamwill not contain any residual errors for adjusting the tweened frames.

Decoding Modes

The decoder can have a number of options for decoding and playing backthe encoded video bitstream. The options allow the decoder to tailor itsperformance adaptively according to the availability of localcomputational resources and the data rates supported at the incomingchannel. The following is a list of some of the different possibledecoding modes of operation:

1. Full Frame Rate Decoding

When the computational resources allow high performance, the decoderwill decode all the H, L, and B frames as outlined above and play theincoming video stream at full resolution and at the full frame rate.

2. Adaptive Creation of B Frames

If the computational resources do not allow top-level performance, thedecoder can start generating tweened B frames at a lower rate. The ratecontrol can be based on the model of interpolation suggested by theencoder. For instance, for constant translation interpolation, a uniformrate of frame dropping may be selected.

3. H and L Frame Decoding Only

This level of operation works with H and L frames only. No tweening isperformed to create B frames. L frames are synthesized to the fullresolution. In extreme cases, some L frames may be dropped to maintainperformance.

4. H Frame Only

In the extreme case, the decoder will resort to H-frame intra-onlydecoding and play the full-resolution frames as a sequence.

Other modes of operation that combine or specialize the above modes arealso possible.

Compression Ratio Calculations

The following presents typical results achieved during compressionprocessing based on the present invention. In the following, B is forbytes and b is for bits.

1. Original uncompressed video digitized as (720×486) pixel frames at 30frames/second (fps).

-   -   349,920 pixels/frame×3 color bytes/pixel×30 fps=>uncompressed        bit rate=31.493 MB/s

2. Temporal sub-sampling of frames to 5 fps (corresponding to selectionof only H and L frames)

-   -   ⅙^(th) of 31.493 MB/s=>5.249 MB/s (for full-resolution H and L        frames)

3. Spatial sub-sampling 4 out of 5 frames to ¼×¼ resolution(corresponding to spatial sub-sampling of L frames)

-   -   ¼th of 5.249 MB/s=1.31 MB/s (for full-resolution H frames and        low-resolution L frames)

4. Color sub-sampling of 4:1:1

-   -   ½ of 1.31 MB/s=0.656 MB/s=656 KB/s

5. Wavelet intra-coding of frames+coding of residuals: Assuming 20:1compression gain in using wavelets to encode H and L frames+10% forencoding residuals=>

-   -   {fraction (1/20)}th of 656 KB/s+10% for encoding residuals˜300        Kbps.

6. For CIF resolution (i.e., 360×243 pixel size frames)

-   -   ¼ of 300 Kbps=75 Kbps        Therefore, for channels with a bandwidth of a few 100 s of Kbps,        the above technique will be quite viable and will produce        results of quality superior to that of conventional codecs. For        channels with lower bandwidth, for example 56K modems, further        sub-sampling in time may be done with some loss of quality or        CIF resolution may be transmitted. For higher bandwidth        channels, further quality improvement may be obtained by        synthesizing B frames at the time of encoding and encoding        residuals between the synthesized and original B frames, e.g.,        using wavelet encoding.        Applications of Generalized Motion Computation at the Decoder        (Client) End

The video compression/decompression scheme described above changes thetraditional paradigm of video codecs. Motion computation capability atthe decoder end enables highly scaleable coding for a wide range ofchannel bandwidths. However, video compression is not the onlycapability enabled by generalized motion computation capability at thedecoder end. A number of innovative capabilities are described in thissection.

1. De-interlacing On-the-fly

Since field-to-field motion is computed at the decoder end, when themotion is per pixel, the motion field can be used to dynamicallycompensate for inter-field motion and create de-interlaced video withoutthe necessity of any other special-purpose hardware. Such de-interlacingcan be used to transparently convert interlaced video for display onprogressive scan displays. The following steps for doing this are allenabled by the generalized decoder described earlier.

-   -   Compute motion between fields.    -   Warp one field towards the other using flow-based warping.    -   Combine the two motion-compensated fields to generate a full        progressive frame.        2. New View Generation On-the-fly

Another attractive application is the generation of novel views giventhe encoded frames in the video stream. Motion estimation capability atthe client/decoder end allows generation of frames that are not a partof the original stream by interpolating between two or more originalframes using the motion fields. In the case of video decoding, thiscapability may be used to generate a full frame-rate video stream from atemporally sub-sampled stream on-the-fly. The same technique enablesuser-controlled generation of new frames either for higher-than-normalframe rates or for providing an experience of navigating through theenvironment.

Consider an immersive reality application in which synchronized videostreams are capturing a dynamic event from many different viewpointsusing a number of cameras. Each of the cameras captures the event fromits own viewpoint. The collection of video streams is multiplexed andcompressed onto a single encoded video bitstream and transmitted to anynumber of clients who wish to experience virtual presence at the site ofthe event. The same decoder capabilities outlined above will allow asystem to decode the multiplexed and time-stamped video streams andspatially “tween” between close-by cameras to allow the user to view thesame event at any time instant from different angles simultaneously.That is, the user is not only able to see a linear traditional video ofthe event, but also freeze any time instant and maneuver around theevent in space and time. In fact, the user can be provided virtualnavigational capability to navigate seamlessly in space and time.

For illustrative purposes, consider that a basketball event is beingcovered by a ring of cameras 902 with reasonable spacing between them,as represented in FIG. 9. The continuum of views along the ring ofcameras can be parameterized, with viewpoint plotted along thehorizontal axis and time plotted along the vertical axis, as representedin FIG. 10. The user may specify any given point in this space-timedomain and the video decoder/renderer will render the view from thespecified viewpoint and at the specified time. In general, a trajectory(e.g., curve 1002 in FIG. 10) through this space-time (i.e., XYZT)domain corresponds to a user moving in the space of views and in time.In addition, any number of viewers can do this independently and atwill.

3. Generalization to Dynamic 3D Viewing under User Control

The above concept of a video decoder as a user-controlled navigator ofenvironments can be further generalized to provide arbitrary detailedcoverage of an environment for remote tele-presence (being there)experiences. Consider a dynamic and complex 3D environment such as theGolden Gate Bridge and its surroundings. Viewers can be provided with animmersive highly photo-realistic experience of being there from theirliving rooms in real time. That is, any number of users can experiencetheir own individual presence through joy-stick-like controls. Everyonesees what they want to see and from what viewpoint.

There are four main generalizations of the streaming video conceptdescribed above:

-   -   (i) The video encoder is a video and dynamic 3D information        encoder.    -   (ii) The encoded stream is a multiplexed and encoded stream that        encodes not just individual frames but shape maps, moving        objects, and the background and other scene-related and        object-related information.    -   (iii) The video decoder is a decoder and an image-based        renderer.    -   (iv) XYZT space-time matrix user interface.        The details of each of these generalizations are outlined in the        following sections.

(i) Dynamic 3D Creator

Each of the real camera views is encoded using wavelet encoding. Inaddition, the local shape information may be encoded. The shapeinformation may include range/parallax maps, moving object versus staticscene layers, foreground/background masks, and the like.

(ii) Dynamic 3D Encoded Stream

Instead of transmitting motion vectors and error residuals as is done inthe current MPEGx and related streams, the dynamic 3D stream consists ofintra-coded frames, and also wavelet-coded range/parallax maps andobject and scene layers. Streams from many different cameras and sensorsare multiplexed together with time stamps.

(iii) Client End Video Decoder/Renderer

The video decoder described earlier for the new streaming videoapplication is generalized here to a video decoder and an image-basedrenderer. All the intra-coded frames are decoded under user control.Furthermore, the shape and layer masks are decoded, and inter-framemotion is computed wherever necessary. A continuous stream ofuser-controlled novel views is generated by shape-based and motion-basedtweening using the time-stamped real views.

(iv) XYZT Space-Time Matrix User Interface

User navigation in the generalized viewing case can be facilitated by afour-dimensional XYZT “cube” that represents the space-time domain ofviewing. In addition, for any given viewpoint, pan, tilt, and zoomcapabilities can also be provided.

4. Real-Time Compositing of Real and Synthetic Content

Another attractive application of the proposed generalized codec schemeis the ability to composite real video content with synthetic 2D and 3Dcontent for on-the-fly rendering at the client end. Since the dynamic 3Dcontent is encoded at the content creation end in terms of foreground,background, and motion layers, compositing capability can be provided atthe viewing (i.e., decoding) end. For instance, virtual billboards couldbe seamlessly inserted into real video streams for targeted marketing.Similarly on-the-fly special effects may be created by insertingsynthetic animated characters into the layered video stream or byreplacing real objects (like faces) by the virtual objects.

Although the present invention has been described in the context ofencoding H frames as full-resolution frames, in alternative embodiments,H frames may be encoded as high-resolution frame, whose resolution islower than that of the original full-resolution H frames, but stillhigher than that of the low-resolution L and B frames.

Although the encoding of the H/L-frame pixel data and B-frame residualerror data has been described as being based on wavelet encoding, thoseskilled in the art will understand that some or all of the wavelet-basedencoding may be replaced by other suitable encoding techniques. Forexample, the encoding could be based on the application of a block-baseddiscrete cosine transform (DCT) following by quantization, run-lengthencoding, and variable-length encoding.

Although the present invention has been described in the context of avideo frame as a single entity, those skilled in the art will understandthat the invention can also be applied in the context of interlacedvideo streams and associated field processing. As such, unless clearlyinappropriate for the particular implementation described, the term“frame,” especially as used in the claims, should be interpreted tocover applications for both video frames and video fields.

The present invention may be implemented as circuit-based processes,including possible implementation on a single integrated circuit. Aswould be apparent to one skilled in the art, various functions ofcircuit elements may also be implemented as processing steps in asoftware program. Such software may be employed in, for example, adigital signal processor, micro-controller, or general-purpose computer.

The present invention can be embodied in the form of methods andapparatuses for practicing those methods. The present invention can alsobe embodied in the form of program code embodied in tangible media, suchas floppy diskettes, CD-ROMs, hard drives, or any other machine-readablestorage medium, wherein, when the program code is loaded into andexecuted by a machine, such as a computer, the machine becomes anapparatus for practicing the invention. The present invention can alsobe embodied in the form of program code, for example, whether stored ina storage medium, loaded into and/or executed by a machine, ortransmitted over some transmission medium or carrier, such as overelectrical wiring or cabling, through fiber optics, or viaelectromagnetic radiation, wherein, when the program code is loaded intoand executed by a machine, such as a computer, the machine becomes anapparatus for practicing the invention. When implemented on ageneral-purpose processor, the program code segments combine with theprocessor to provide a unique device that operates analogously tospecific logic circuits.

It will be further understood that various changes in the details,materials, and arrangements of the parts which have been described andillustrated in order to explain the nature of this invention may be madeby those skilled in the art without departing from the principle andscope of the invention as expressed in the following claims.

1. A method for encoding a video stream to generate an encoded videobitstream, comprising the steps of: (a) encoding, into the encoded videobitstream, a first original frame/region in the video stream usingintra-frame coding to generate an encoded first frame/region; and (b)encoding, into the encoded video bitstream, a second originalframe/region in the video stream using motion-based predictive coding,wherein: the motion-based predictive coding comprises motion computationadapted to generate motion information using during the motion-basedpredictive coding; and at least some of the motion information usedduring the motion-based predictive coding is excluded from the encodedvideo bitstream.
 2. The invention of claim 1, wherein all of the motioninformation used during the motion-based predictive coding is excludedfrom the encoded video bitstream and the encoded video bitstream doesnot explicitly include any motion information.
 3. The invention of claim1, wherein step (b) comprises the steps of: (1) decoding the encodedfirst frame/region to generate a decoded first frame/region; (2)encoding the second original frame/region to generate an encoded secondframe/region; (3) decoding the encoded second frame/region to generate adecoded second frame/region; (4) performing motion computation betweenthe decoded second frame/region and the decoded first frame/region togenerate the motion information; (5) applying the motion information tothe decoded first frame/region to generate a synthesized secondframe/region; (6) performing inter-frame differencing between thesynthesized second frame/region and the second original frame/region togenerate residual errors; and (7) encoding, into the encoded videobitstream, at least some of the residual errors.
 4. The invention ofclaim 1, further comprising the step of: (c) encoding, into the encodedvideo bitstream, a third original frame/region in the video stream usingtweening based on the motion information used to encode the secondoriginal frame/region.
 5. The invention of claim 1, wherein themotion-based predictive coding comprises: motion computation duringwhich one or more motion vectors are determined for the second originalframe/region; and motion compensation based on the one or more motionvectors determined during motion computation, wherein at least one ofthe motion vectors used during the motion compensation is excluded fromthe encoded video bitstream.
 6. The invention of claim 5, wherein eachmotion vector used during the motion compensation is excluded from theencoded video bitstream.
 7. A video encoder for encoding a video streamto generate an encoded video bitstream, comprising: (a) a frame/regiontype selector configured for selecting different processing paths forencoding different frames/regions into the encoded video bitstream; (b)a first processing path configured for encoding, into the encoded videobitstream, a first original frame/region in the video stream usingintra-frame coding to generate an encoded first frame/region; and (c) asecond processing path configured for encoding, into the encoded videobitstream, a second original frame/region in the video stream usingmotion-based predictive coding, wherein: the motion-based predictivecoding comprises motion computation adapted to generate motioninformation using during the motion-based predictive coding; and thevideo encoder has an encoding mode in which at least some of the motioninformation used during the motion-based predictive coding is excludedfrom the encoded video bitstream.
 8. The invention of claim 7, whereinthe video encoder is a scaleable video encoder that can be operated at aplurality of different encoding modes, wherein: in a first encodingmode, all of the motion information is excluded from the encoded videobitstream and the encoded video bitstream does not explicitly includeany motion information; and in a second encoding mode, at least some ofthe motion information is encoded into the encoded video bitstream. 9.The invention of claim 8, wherein: in the second encoding mode, a firstportion of the motion information is encoded into the encoded videobitstream and a second portion of the motion information is excludedfrom the encoded video bitstream; and in a third encoding mode, all ofthe motion information is encoded into the encoded video bitstream. 10.The invention of claim 7, wherein: the first processing path isconfigured for decoding the encoded first frame/region to generate adecoded first frame/region; and the second processing path is configuredfor: (1) encoding the second original frame/region to generate anencoded second frame/region; (2) decoding the encoded secondframe/region to generate a decoded second frame/region; (3) performingmotion computation between the decoded second frame/region and thedecoded first frame/region to generate the motion information; (4)applying the motion information to the decoded first frame/region togenerate a synthesized second frame/region; (5) performing inter-framedifferencing between the synthesized second frame/region and the secondoriginal frame/region to generate residual errors; and (6) encoding,into the encoded video bitstream, at least some of the residual errors.11. The invention of claim 10, wherein the encoding in the firstprocessing path and the encoding of the second original frame/region inthe second processing path are based on intra-frame wavelet encoding.12. The invention of claim 10, wherein: the first processing path isconfigured for intra-frame coding the first original frame/region at ahigh resolution; the decoded first frame/region is at the highresolution; the second processing path is configured for: (i) spatiallysub-sampling the second original image/region to generate alow-resolution second frame/region having a resolution lower than thehigh resolution; and (ii) intra-frame coding the low-resolution secondframe/region to generate the encoded second frame/region; the decodedsecond frame/region is at the low resolution; and the synthesized secondframe/region is at the high resolution.
 13. The invention of claim 10,wherein the second processing path is configured for: (i) thresholdingthe residual errors to generate binary data; and (ii) encoding, into theencoded video bitstream, the at least some of the residual errors basedon the binary data.
 14. The invention of claim 7, further comprising athird processing path configured for encoding, into the encoded videobitstream, a third original frame/region in the video stream usingtweening based on the motion information used to encode the secondoriginal frame/region.
 15. The invention of claim 14, wherein: the firstprocessing path is configured for decoding the encoded firstframe/region to generate a decoded first frame/region; and the thirdprocessing path is configured for: (1) temporally interpolating themotion information used to encode the second original frame/region; (2)applying the temporally interpolated motion information to the decodedfirst frame/region to generate a synthesized third frame/region; (3)generating residual errors between the synthesized third frame/regionand the third original frame/region; and (4) encoding, into the encodedvideo bitstream, at least some of the residual errors.
 16. The inventionof claim 15, wherein: the first processing path is configured forintra-frame coding the first original frame/region at a high resolution;the decoded first frame/region is at the high resolution; thesynthesized third frame/region is at the high resolution; and the thirdprocessing path is configured for performing inter-frame differencingbetween the synthesized third frame/region and the third originalframe/region to generate the residual errors.
 17. A method for decodingan encoded video bitstream to generate a decoded video stream,comprising the steps of: (a) decoding, from the encoded video bitstream,an encoded first frame/region using intra-frame decoding to generate adecoded first frame/region; and (b) decoding, from the encoded videobitstream, an encoded second frame/region using motion-based predictivedecoding, wherein at least some motion information used during themotion-based predictive decoding is generated by performing motioncomputation as part of the decoding method.
 18. The invention of claim17, wherein the encoded video bitstream does not explicitly include anymotion information and all of the motion information used during themotion-based predictive decoding is generated as part of the method. 19.The invention of claim 17, wherein step (b) comprises the steps of: (1)decoding, from the encoded video bitstream, the encoded secondframe/region to generate a decoded second frame/region; (2) performingthe motion computation between the decoded second frame/region and thedecoded first frame/region to generate the motion information; (3)applying the motion information to the decoded first frame/region togenerate a synthesized second frame/region; (4) decoding, from theencoded video bitstream, encoded residual errors to generate decodedresidual errors corresponding to the synthesized second frame/region;and (5) performing inter-frame addition between the decoded residualerrors and the synthesized second frame/region to generate anerror-corrected decoded second frame/region.
 20. The invention of claim17, further comprising the step of: (c) generating a decoded thirdframe/region using tweening based on the motion information used todecode the encoded second frame/region.
 21. The invention of claim 17,further comprising the step of de-interlacing a decoded secondframe/region generated during step (b) to generate two correspondingfields corresponding to the decoded second frame/region.
 22. A videodecoder for decoding an encoded video bitstream to generate a decodedvideo stream, comprising: (a) a frame/region type selector configuredfor selecting different processing paths for decoding different encodedframes/regions from the encoded video bitstream; (b) a first processingpath configured for decoding, from the encoded video bitstream, anencoded first frame/region in the video stream using intra-framedecoding to generate a decoded first frame/region; and (c) a secondprocessing path configured for decoding, from the encoded videobitstream, an encoded second frame/region in the video stream usingmotion-based predictive decoding, wherein the video decoder has adecoding mode in which at least some motion information used during themotion-based predictive decoding is generated by the video decoderperforming motion computation.
 23. The invention of claim 17, whereinthe motion-based predictive decoding further comprises motioncompensation for the encoded second frame/region based on one or moremotion vectors, wherein at least one of the motion vectors used duringthe motion compensation is determined during the motion computation. 24.The invention of claim 23, wherein each motion vector used during themotion compensation is determined during the motion computation.
 25. Theinvention of claim 22, wherein the video decoder is a scaleable videodecoder that can be operated at a plurality of different decoding modes,wherein: in a first decoding mode, the encoded video bitstream does notexplicitly include any motion information and all of the motioninformation is generated by performing the motion computation by thevideo decoder; and in a second decoding mode, at least some of themotion information is decoded from the encoded video bitstream.
 26. Theinvention of claim 25, wherein: in the second decoding mode, a firstportion of the motion information is decoded from the encoded videobitstream and a second portion of the motion information is generated byperforming the motion computation by the video decoder; and in a thirddecoding mode, all of the motion information is decoded from the encodedvideo bitstream.
 27. The invention of claim 22, wherein: the secondprocessing path is configured for: (1) decoding, from the encoded videobitstream, the encoded second frame/region to generate a decoded secondframe/region; (2) performing the motion computation between the decodedsecond frame/region and the decoded first frame/region to generate themotion information; (3) applying the motion information to the decodedfirst frame/region to generate a synthesized second frame/region; (4)decoding, from the encoded video bitstream, encoded residual errors togenerate decoded residual errors corresponding to the synthesized secondframe/region; and (5) performing inter-frame addition between thedecoded residual errors and the synthesized second frame/region togenerate an error-corrected decoded second frame/region.
 28. Theinvention of claim 27, wherein the decoding in the first processing pathand the decoding of the second encoded frame/region in the secondprocessing path are based on intra-frame wavelet decoding.
 29. Theinvention of claim 27, wherein: the decoded first frame/region is at ahigh resolution; the decoded second frame/region is at a low resolutionlower than the high resolution; the synthesized second frame/region isat the high resolution; and the error-corrected decoded secondframe/region is at the high resolution.
 30. The invention of claim 22,further comprising a third processing path configured for generating adecoded third frame/region using tweening based on the motioninformation used to decode the encoded second frame/region.
 31. Theinvention of claim 30, wherein the third processing path is configuredfor: (1) temporally interpolating the motion information used to decodethe encoded second frame/region; and (2) applying the temporallyinterpolated motion information to the decoded first frame/region togenerate the decoded third frame/region.
 32. The invention of claim 31,wherein the decoded third frame/region is not explicitly represented inthe encoded video bitstream.
 33. The invention of claim 31, wherein thethird processing path is configured for: (i) applying the temporallyinterpolated motion information to the decoded first frame/region togenerate a synthesized third frame/region; (ii) decoding, from theencoded video bitstream, encoded residual errors for an encoded thirdframe/region to generate decoded residual errors; and (iii) applying thedecoded residual errors to the synthesized third frame/region togenerate the decoded third frame/region.
 34. The invention of claim 33,wherein: the decoded first frame/region is at a high resolution; thesynthesized third frame/region is at the high resolution; and the thirdprocessing path is configured for performing inter-frame additionbetween the synthesized third frame/region and the decoded residualerrors to generate the decoded third frame/region at the highresolution.
 35. The invention of claim 22, wherein the second processingpath is configured for de-interlacing a decoded second frame/region togenerate two corresponding fields corresponding to the decoded secondframe/region.